The development of penicillin started – but definitely did not end – with the chance discovery of some mold in a petri dish. There is so much more to the story.
Research:

Percy Fawcett, Manuscript 512, and a Lost City in the Amazon, Pt. 2
37:10

Percy Fawcett, Manuscript 512, and a Lost City in the Amazon, Pt. 1
34:05

SYMHC Classics: Swill Milk
39:22